Data communications to and from traveling vehicles have attracted increasing attention in the communication and automotive industries. This attention has led to the development of the IEEE 802.11p amendment to the 802.11 wireless local area network (WLAN) family of standards. IEEE 802.11p was defined to add wireless access in vehicular environments (WAVE), and specifies enhancements to the basic 802.11 standard that are useful in supporting Intelligent Transportation System (ITS) applications.
The physical layer (PHY) of IEEE 802.11p uses the frame format and data encoding scheme that were specified originally by IEEE 802.11a, based on orthogonal frequency-domain multiplexing (OFDM). A frame in this context is referred to as a PHY protocol data unit (PPDU). The PPDU format defined in section 17.3.2 of IEEE Draft Standard IEEE P802.11REVmc™/D8.0 (August 2016) includes predefined pilot signals inserted by the transmitting PHY in sub-carriers −21, −7, 7 and 21, out of a total of 52 sub-carriers in each OFDM symbol. The receiving PHY detects and processes these known pilot signals for the purpose of common phase estimation and compensation (CPE/C).
The use of “traveling pilots” has been proposed as an alternative pilot scheme for OFDM communications, in place of schemes in which pilot signals are inserted in a fixed set of sub-carriers. For example, U.S. Patent Application Publication 2016/0013908 describes a scheme in which pilot tones occupy fewer than all tone locations in any given symbol, and the pilot tones occupy different respective locations within different symbols. Generally, these traveling pilots are assigned to different respective tone locations in different symbols. In total, the pilot tones do not cover every single tone location within the symbols used to convey information between devices. Considering for example, when pilots occupy fewer than all tone locations, even among multiple symbols, a device may perform interpolation to generate a pilot tone estimate corresponding to a tone location not occupied by pilot tone within any symbol.